Journal articles on the topic 'Degree of silica hydration'
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1
Bach, Quoc Si. "Investigation of Blended Cement Hydration in the Reactive Powder Concrete with Increasing Levels of Silica Fume Addition." Applied Mechanics and Materials 889 (March 2019): 304–12. http://dx.doi.org/10.4028/www.scientific.net/amm.889.304.
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Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydration products. By the process of hydration Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. The Therefore, the concrete properties always accompanies with the hydration degree of cement. This paper presents some experimental test results on how silica fume affects the cement hydration in cement pastes of the Reactive Powder Concrete as increasing levels of silica fume addition with the content from 0% to 30% of cement mass. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, rate of heat evolution, of binder pastes obtained by isothermal calorimetry (TAM-Air). In addition, the portlandite content, the hydration degree of pure cement, reaction degree of binder paste as well as reaction degree of silica fume were investigated. The quantitative assessment on these characteristics are due to the simulation of the hydration of Portland cement pastes containing silica fume.
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Wu, Cheng Zhu, Yong He Liang, Yu Cheng Yin, Man Fei Cai, Jian Hua Nie, and Sen Cai Shen. "Characterization of Hydrolysis Process of a Silane Coupling Agent KH-570." Key Engineering Materials 768 (April 2018): 279–85. http://dx.doi.org/10.4028/www.scientific.net/kem.768.279.
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The hydrolysis process of a silane coupling agent KH-570 in deionized water, ethanol, and their mixed medium was characterized by continuous online conductivity testing, respectively. In addition, hydration products of KH-570 in different mediums were analyzed by Fourier transform infrared spectroscopy (FTIR) to correlate with its hydration process. Results indicate that the KH-570 hydrates fast and to a large degree in deionized water, but at the same time, its hydrolysis products condensate together with increasing rate during the hydration process. However, the introduction of ethanol could significantly reduce the degree of the condensation. The hydrolysis degree of KH-570 was relatively large in a mix medium of deionized water and ethanol with the mass ratio of 5:1, and condensation degree of hydrolysis products was also small. KH-570 would hydrate quickly in a hydration medium of colloidal silica, and subsequently, its hydration products would directly react with colloidal silica, which could accelerate the formation of Si-O-Si three-dimensional network structure, and thus promoting the setting of colloidal silica. The hydration of 0.9wt% KH-570 in colloidal silica could be sufficient, and correspondingly, its effect on the coagulation of colloidal silica was better.
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Wang, Feng, Pingan Chen, Xiangcheng Li, and Boquan Zhu. "Effect of Colloidal Silica on the Hydration Behavior of Calcium Aluminate Cement." Materials 11, no. 10 (September 28, 2018): 1849. http://dx.doi.org/10.3390/ma11101849.
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The effect of colloidal silica (CS) on the hydrate phases and microstructure evolution of calcium aluminate cement (CAC) was investigated. Samples hydrated with CS were obtained and characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared spectroscopy (FT-IR), hydration heat measurement and Nuclear Magnetic Resonance (NMR). The results revealed that SiO2 nanoparticles may affect the hydrates crystallization process. There was a compact structure in the CAC paste with CS, while petal-shaped hydrates with a porous structure were formed in the pure CAC paste. The maximum value of electrical conductivity for CAC paste with CS suggested that the early stage of hydration for CAC was accelerated. However, the hydration heat curves revealed that the late stage of the CAC hydration process was inhibited, and the hydration degree was reduced, this result was in accordance with Thermogravimetry-Differential scanning calorimetry(TG-DSC) curves. The fitting results of hydration heat curves further showed that the hydration degree at NG (nucleation and crystal growth) process stage was promoted, while it was limited at the phase boundaries stage, and the diffusion stage in the hydration reaction was brought forward due to the addition of CS. According to these results and analyses, the differences in the hydration process for CAC with and without CS can be attributed to the distribution and nucleation effect of SiO2 nanoparticles.
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Skripkiūnas, Gintautas, Žymantas Rudžionis, and Vitoldas Vaitkevičius. "COMPLEX ADMIXTURES FOR HIGH-STRENGTH CONCRETE." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 8, no. 4 (December 31, 2002): 276–80. http://dx.doi.org/10.3846/13923730.2002.10531288.
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The influence of naphthalene formaldehyde superplasticizers (NFS), lignosulfonate plasticizers (LSP) and silica fume on cement paste properties and complex usage of these admixtures for high-strength concrete production are investigated in this research. These admixtures influence the cement hydration products morphology and properties of hardened cement paste. The degree of cement hydration and Ca(OH)2 content in hardened cement paste were determined for analysis of cement hydration process with admixtures. Mechanical properties and porosity of hardened cement paste with the admixtures were tested. Optimal dosages of plasticizing admixtures and silica fume were estimated and the most efficient method of silica fume adding to concrete mixture was proposed. The results of investigation have been used for high-strength concrete production.
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Huang, Ruixing, Chengxue Ma, Qiang He, Jun Ma, Zhengsong Wu, and Xiaoliu Huangfu. "Ion specific effects of monovalent cations on deposition kinetics of engineered nanoparticles onto the silica surface in aqueous media." Environmental Science: Nano 6, no. 9 (2019): 2712–23. http://dx.doi.org/10.1039/c9en00251k.
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Kang, Hyunuk, Nankyoung Lee, and Juhyuk Moon. "Elucidation of the Hydration Reaction of UHPC Using the PONKCS Method." Materials 13, no. 20 (October 19, 2020): 4661. http://dx.doi.org/10.3390/ma13204661.
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This study explored the hydration reaction of ultra-high-performance concrete (UHPC) by using X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA) as analysis methods. The partial- or no-known crystal structure (PONKCS) method was adopted to quantify the two main amorphous phases of silica fume and C-S-H; such quantification is critical for understanding the hydration reaction of UHPC. The measured compressive strength was explained well by the degree of hydration found by the PONKCS method, particularly the amount of amorphous C-S-H. During heat treatment, the pozzolanic reaction was more intensified by efficiently consuming silica fume. After heat treatment, weak but continuous hydration was observed, in which the cement hydration reaction was dominant. Furthermore, the study discussed some limitations of using the PONKCS method for studying the complicated hydration assemblage of UHPC based on the results of TGA and NMR. Generally, the PONKCS method underestimated the content of silica fume in the early age of heat treatment. Furthermore, the structural evolution of C-S-H, confirmed by NMR, should be considered for more accurate quantification of C-S-H formed in UHPC. Nevertheless, PONKCS-based XRD could be useful for understanding and optimizing the material properties of UHPC undergoing heat treatment.
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Turov, V. V., V. M. Gun'ko, and T. V. Krupska. "Methane adsorption onto silicas with various degree of hydrophobicity." Surface 13(28) (December 30, 2021): 94–126. http://dx.doi.org/10.15407/surface.2021.13.094.
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The methane adsorption onto a hydrated surface of hydrophobic silica AM1 alone and impregnated by arginine, and silica gel Si-100 has been studied using low-temperature 1H NMR spectroscopy. It has been shown that the methane adsorption onto the AM1 surface depends on the degree of hydration and pretreatment type. The maximum adsorption (up to 80 mg/g) is observed for a sample hydrated after complete drying. It has been established that the adsorption is determined by a number of clusters of bound water of small radii. Based on a shape of the temperature dependence of the adsorption, it has been assumed that not only physical adsorption occurs, but also the quasi-solid methane hydrates are formed. It has been established that the amount of methane adsorbed onto a surface of a composite system AM1/arginine under isobaric conditions increases by tens of times (from 0.5 to 80 mg/g) in the presence of pre-adsorbed water pre-adsorbed at the surface. Probable mechanisms of the methane adsorption are physical adsorption on a surface, condensation in narrow voids between silica nanoparticles and nano-scaled (1-10 nm) water clusters, and the formation of solid (clathrate) methane hydrates. Water, adsorbed at a surface in a wide range of hydration, forms various clusters. This water is mainly strongly associated and characterized by chemical shifts in the range dH = 4-6 ppm. The hydrate structures with methane/water are quite stable and can exist even in the chloroform medium. However, in this case, a part of water transforms into a weakly associated state and it is observed at dH = 1.5-2 ppm.
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Zhou, Yue, Zhongping Wang, Zheyu Zhu, Yuting Chen, Linglin Xu, and Kai Wu. "Impacts of Space Restriction on the Microstructure of Calcium Silicate Hydrate." Materials 14, no. 13 (June 30, 2021): 3645. http://dx.doi.org/10.3390/ma14133645.
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The effect of hydration space on cement hydration is essential. After a few days, space restriction affects the hydration kinetics which dominate the expansion, shrinkage and creep of cement materials. The influence of space restriction on the hydration products of tricalcium silicate was studied in this paper. The microstructure, morphology and composition of calcium silicate hydrate (C-S-H) were explored from the perspective of a specific single micropore. A combination of Raman spectra, Fourier transform infrared spectra, scanning electron microscopy and energy dispersive X-ray spectroscopy were employed. The results show that space restriction affects the structure of the hydration products. The C-S-H formed in the micropores was mainly composed of Q3 silicate tetrahedra with a high degree of polymerization. The C-S-H formed under standard conditions with a water to cement ratio of 0.5 mostly existed as Q2 units. Space restriction during hydration is conducive to the formation of C-S-H with silica tetrahedra of a high polymerization degree, while the amount of water filling the micropore plays no obvious role on the polymeric structure of C-S-H during hydration.
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Pyeon, Sujeong, Gyuyong Kim, Sangsoo Lee, and Jeongsoo Nam. "Internal Curing Effect of Waste Glass Beads on High-Strength Cement Composites." Applied Sciences 12, no. 16 (August 22, 2022): 8385. http://dx.doi.org/10.3390/app12168385.
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High-strength concrete (HSC) uses binders and microfillers with ultrafine particles, such as silica fume. The resulting dense internal hydration structure rapidly decreases HSC humidity, causing shrinkage cracks and affecting internal hydration. Herein, the hydration degree inside high-strength cement composites (HSCCs) was examined using waste glass beads (WGBs) as lightweight aggregates (LWAs). Moreover, unreacted hydrate reduction and hydrate formation tendencies were investigated. WGBs with particle sizes within 2.00–6.00 mm were added at ratios of 5%, 10%, and 20% after pre-wetting. The increased number of hydrates inside the specimens were examined under steam curing (80 °C) and room temperature curing (25 °C). The strength decreased as the WGB content increased. Thermogravimetric, X-ray diffraction, and Si nuclear magnetic resonance analyses revealed that the hydration degree of Si inside HSCCs changed when the content of pre-wetted LWAs changed. A visual inspection of the specimen cross-section and scanning electron microscopy–energy-dispersive X-ray spectrometry (SEM–EDS) analysis revealed the moisture trapped inside WGB pores and the hydration tendency. Under steam curing and room temperature curing, the paste contained different amounts of hydrates, depending on WGB content. Moreover, water-absorbed WGBs were continuously desorbed through SEM–EDS, and hydrates were present in WGB pores.
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Zhou, Haiyun, Hongbo Zhu, Hongxiang Gou, and Zhenghong Yang. "Comparison of the Hydration Characteristics of Ultra-High-Performance and Normal Cementitious Materials." Materials 13, no. 11 (June 6, 2020): 2594. http://dx.doi.org/10.3390/ma13112594.
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The hydration mechanism of ultra-high-performance cementitious materials (UHPC) departs considerably from that of normal cementitious materials (NC). In this study, the strength, isothermal calorimetry, chemical shrinkage, X-ray diffraction (XRD), and thermogravimetry (TG) methods are used to determine the hydration characteristics of UHPC and NC that contain silica fume (SF). A simple device was modified to test the chemical shrinkage for long-term growth, and the ultimate chemical shrinkage is obtained by semi-empirical formula fitting. It is found that the degree of hydration of UHPC is significantly lower than that of NC. The hydration kinetics analyzed using the Krstulovic-Dabic model shows that the hydration process of NC is type NG-I-D, which is characterized by gentle and prolonged hydration. However, the hydration of UHPC is type NG-D with the distinguishing features of early sufficiency and later stagnation. The growth of the strength, exothermic evolution, and phase development of UHPC is decelerated as the hydration process proceeds, which confirms the weak development tendency of hydration at the later stage. In addition, the effect of SF on the hydration of UHPC is minor, and the higher content of SF is beneficial to the hydration at the later stage.
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Cheng, Fuan, Yaru Hu, Qiang Song, Jiao Nie, Jiahao Su, and Yanxin Chen. "Effect of Curing Temperature on the Properties of a MgO-SiO2-H2O System Prepared Using Dead-Burned MgO." Materials 15, no. 17 (September 1, 2022): 6065. http://dx.doi.org/10.3390/ma15176065.
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The hydration of M-S-H prepared using silica fume (SF) and dead-burned MgO cured at 20 °C, 50 °C, and 80 °C was investigated, and the properties and performance of this M-S-H were measured. The formation of M-S-H was characterized using XRD, FTIR, TGA, and 29Si MAS-NMR. Results show that the compressive strength of paste prepared using MgO calcined at 1450 °C for 2 h reached 25 MPa after 28 d. The shrinkage of mortar made with low reactivity MgO was lower than that made with high reactivity MgO. The pH value of MgO/SF paste mixed with dead-burned MgO did not exceed 10.4 at room temperature. The shrinkage of M-S-H prepared using dead-burned MgO was less than that prepared using more active MgO, and its strength did not decrease over time. No (or only a small amount of) Mg(OH)2 was formed, which is why the strength of M-S-H prepared with dead-burned MgO continually increased, without decreasing. The promotion of curing temperature favor process of MgO hydration and is beneficial for degree of silica polymerization. The sample cured in 50 °C water showed the highest relative degree of reaction.
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Wu, Weilv, Wenbin Xu, and Yalun Zhang. "Measuring Ultrasonic and Electrical Properties of Early-Age Cemented Tailings Backfill." Minerals 13, no. 2 (January 17, 2023): 135. http://dx.doi.org/10.3390/min13020135.
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The setting behavior strongly affects the workability and loading capacity of a fresh cemented tailings backfill (CTB). The Vicat test is a conventional way to measure the setting time of a fresh cementitious mixture, using a standard needle to detect penetration resistance. However, this method is limited to laboratory testing, it is difficult to carry out in underground closed stopes. In this study, two nondestructive methods, the ultrasonic pulse and electrical conductivity tests, contrasting two traditional methods, hydration heat measurement and the Vicat test, are used to illustrate the setting process of early-age CTB. The effect of cement content (e.g., 2.5, 5 and 7.5%) and tailings type (silica tailings and iron mine tailings) on the hydration heat of early-age CTB are recorded as well. The results show that, as the CTBs change from solid–liquid mixtures to solids, the ultrasonic pulse frequency converts from low to high and the electrical conductivity turns from growth to decline. As the degree of hydration increases, the solid connections continuously increase, which increases the ultrasonic amplitude rapidly and decreases electrical conductivity. The TG value can be effectively used to predict the initial set time of cemented silica tailings backfill. For cemented iron tailings backfill, although the solid phase ultrasonic path is formed, more hydration products are needed to reach the specific shear stiffness, meaning the initial set lags behind the change in ultrasonic frequency signal.
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Wang, Jie, Xuesong Lu, Baoguo Ma, and Hongbo Tan. "Cement-Based Materials Modified by Colloidal Nano-Silica: Impermeability Characteristic and Microstructure." Nanomaterials 12, no. 18 (September 13, 2022): 3176. http://dx.doi.org/10.3390/nano12183176.
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Colloidal nano-silica (CNS) was used to improve the mechanical and impermeability characteristics of mortar in this study. The samples were prepared with 0%, 1%, 2% and 3% (solid content) CNS addition. The mechanical strength and permeability of each mixture was studied, and the mechanism behind was revealed by hydration heat evolution, XRD, DSC-DTG, 29Si MAS-NMR and SEM-EDS analysis. The compressive strength and impermeability characteristics of mortars incorporating CNS were significantly improved. The experimental results demonstrated that the incorporation of CNS promoted the early hydration process of cement, thus increasing the polymerization degree of hydrated calcium silicate, decreasing the porosity, and improving the microstructure of mortar. Furthermore, 3% CNS decreased the Ca/Si ratio of the interfacial transition zone (ITZ) from 3.18 to 2.22, thus the enrichment of CH was reduced and the density and strength were improved. This was mainly because of the high pozzolanic activity of CNS, which consumed plenty of calcium hydroxide and converted to C-S-H. Besides, nanoscale CNS and C-S-H particles filled the voids between hydrates, thus refining the pore size, increasing the complexity of pores, and improving the microstructure of ITZ which contributed to the improvement of the impermeability.
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Ramesh, Sivarajan, Israel Felner, Yuri Koltypin, and Aharon Gedanken. "Reaction Pathways at the Iron–microspherical Silica Interface: Mechanistic Aspects of the Formation of Target Iron Oxide Phases." Journal of Materials Research 15, no. 4 (April 2000): 944–50. http://dx.doi.org/10.1557/jmr.2000.0135.
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Oxidative hydrolysis of elemental iron nanoclusters on hydroxylated surfaces such as silica or alumina is known to be influenced by the degree of hydration of the surface. The understanding and control of this process is crucial in the synthesis of iron oxide coated silica microspheres with a desired magnetic property. The hydrolysis of iron nanoparticles followed by heat treatment in the case of a hydrated microspherical silica surface results in the formation of maghemite (γ–Fe2O3), whereas a dehydrated surface yielded hematite (α–Fe2O3) nanoparticles. The influence of adsorbed water on the formation of intermediate iron oxides/oxidehydroxides and the mechanistic aspects of their subsequent thermal dehydration iron oxide phases were investigated by thermogravimetric analysis, Fourier transform infrared, and Mössbauer spectroscopies. The reactions on both the hydrated and the dehydrated surfaces were found to proceed through the formation of an x-ray amorphous lepidocrocite [γ–FeO(OH)] intermediate and its subsequent dehydration to maghemite (γ–Fe2O3). Maghemite to hematite transformation was readily facilitated only on a dry silica surface. The retardation of the lepidocrocite →maghemite →hematite transformation in the case of a hydrated silica surface is suggested to arise from strong hydrogen-bonded interactions between the substrate silica and the adsorbed nanoparticles.
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Ling, Gang, Zhonghe Shui, Tao Sun, Xu Gao, Yunyao Wang, Yu Sun, Guiming Wang, and Zhiwei Li. "Rheological Behavior and Microstructure Characteristics of SCC Incorporating Metakaolin and Silica Fume." Materials 11, no. 12 (December 18, 2018): 2576. http://dx.doi.org/10.3390/ma11122576.
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This study explores the effects of metakaolin (MK) and silica fume (SF) on rheological behaviors and microstructure of self-compacting concrete (SCC). The rheology, slump flow, V-funnel, segregation degree (SA), and compressive strength of SCC are investigated. Microstructure characteristics, including hydration product and pore structure, are also studied. The results show that adding MK and SF instead of 4%, 6% and 8% fly ash (FA) reduces flowability of SCC; this is due to the fact that the specific surface area of MK and SF is larger than FA, and the total water demand increases as a result. However, the flowability increases when replacement ratio is 2%, as the small MK and SF particles will fill in the interstitial space of mixture and more free water is released. The fluidity, slump flow, and SA decrease linearly with the increase of yield stress. The total amount of SF and MK should be no more than 6% to meet the requirement of self-compacting. Adding MK or SF to SCC results in more hydration products, less Ca(OH)2 and refinement of pore structure, leading to obvious strength and durability improvements. When the total dosage of MK and SF admixture is 6%, these beneficial effects on workability, mechanical performance, and microstructure are more significant when SF and MK are applied together.
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Liu, Haibao, Qiuyi Li, Dunlei Su, Gongbing Yue, and Liang Wang. "Study on the Influence of Nanosilica Sol on the Hydration Process of Different Kinds of Cement and Mortar Properties." Materials 14, no. 13 (June 30, 2021): 3653. http://dx.doi.org/10.3390/ma14133653.
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Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar.
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Wu, Qing, Yan Zou, Jianhua Gu, Jun Xu, Rongjian Ji, and Gang Wang. "The Influence and Action Mechanization of Mineral Mixed Material on High Fluidity Potassium Magnesium Phosphate Cement (MKPC)." Journal of Composites Science 4, no. 1 (March 19, 2020): 29. http://dx.doi.org/10.3390/jcs4010029.
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Potassium magnesium phosphate cement (MKPC) is a type of chemically bonded ceramic material that has higher performance compared to traditional Portland cement. To develop the spraying and crack pouring process of MKPC, the mechanical properties, volume deformation, hydration temperature, and water stability of the high-fluidity MKPC with different mineral mixed materials and their influence laws were studied. The effects of phase composition and micromorphology of hydration products on the properties of MKPC and its mechanism were analyzed using X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM). The results show that fly ash and metakaolin will not reduce the fluidity of MKPC paste because of their material properties, and silica fume will reduce the fluidity of MKPC paste because of its large specific surface area and high water absorption. Metakaolin can react with phosphate to form aluminum phosphate gel and fill the pores between the crystals because it has a higher activity, which can significantly improve its compressive strength. However, during the later stage of hydration, there will be slight expansion, which would reduce its bonding flexural strength. The MKPC-hardened paste mixed with silicon ash has optimal stability: therefore, it has the highest bonding flexural strength. Microcosmic analysis shows that mineral mixed material plays a physical filling role and participates in the hydration reaction as an active ingredient to improve the early hydration degree, which can change the crystal size and micromorphology of MKPC-hardened paste and make the structure more compact.
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Yang, Menghui, Zhen He, Xia Chen, Mingxia Li, and Ziling Peng. "Comparative Study on the Macroscopic and Microscopic Properties of UHPC Mixed with Limestone Powder and Slag Powder." Geofluids 2021 (April 6, 2021): 1–11. http://dx.doi.org/10.1155/2021/5510490.
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This paper explores the development laws of the fluidity, compressive strength, and autogenous shrinkage of ultrahigh performance cement (UHPC) mixed with limestone powder (LP) and highly active ground slag powder (SP). A microscopic analysis was conducted on the hydration products and pore structures. Through quantitative research on the packing density and fractal dimension of particles in different systems, the relationship between particle characteristics and UHPC properties was established. As a result, the packing densities of the UHPC mixed solely with LP (binary system) and UHPC mixed with LP and silica fume (ternary system) are higher than those of UHPC mixed with the same amount of SP and the benchmark UHPC system; fractal dimension of particle size distribution is closely related to packing density. The LP-cement-silica fume ternary system was lowly hydrated, but it has a good grain composition and high density of slurry, which improved the compressive strength of UHPC. The compressive strength of UHPC mixed with 50% LP witnessed a more obvious decline than that of the ternary system and the one with the same amount of SP. The reason lies in the decrease in slurry due to a lack of sufficient active constituents, and the hydration products were far from enough to fill the pores in the system. LP can also inhibit autogenous shrinkage to the greatest degree for the LP-mixed binary system performed best in such inhibition.
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Liu, Hengrui, Xiao Sun, Yao Wang, Xueying Lu, Hui Du, and Zhenghong Tian. "Study on the Influence of Silica Fume (SF) on the Rheology, Fluidity, Stability, Time-Varying Characteristics, and Mechanism of Cement Paste." Materials 15, no. 1 (December 23, 2021): 90. http://dx.doi.org/10.3390/ma15010090.
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In this study, the rheology, fluidity, stability, and time-varying properties of cement paste with different substitute contents of silica fume (SF) were investigated. The result showed that the effects of SF on macro-fluidity and micro-rheological properties were different under different water–cement ratios. The addition of SF increased the yield stress and plastic viscosity in the range of 2.61–18.44% and 6.66–24.66%, respectively, and reduced the flow expansion in the range of 4.15–18.91%. The effect of SF on cement paste gradually lost its regularity as the w/c ratio increased. The SF can effectively improve the stability of cement paste, and the reduction range of bleeding rate was 0.25–4.3% under different water–cement ratios. The mathematical models of rheological parameters, flow expansion, and time followed the following equations: τ(t) = τ0 + k0t, η(t) = η0eat, and L(t) = L0 − k1t, L(t) = L0 − k1t − a1t2. The SF slowly increased the rheological parameters in the initial time period and reduced the degree of fluidity attenuation, but the effect was significantly enhanced after entering the accelerated hydration period. The mechanism of the above results was that SF mainly affected the fluidity and rheology of the paste through the effect of water film thickness. The small density of SF particles resulted in a low sedimentation rate in the initial suspended paste, which effectively alleviated the internal particle agglomeration effect and enhanced stability. The SF had a dilution effect and nucleation effect during hydration acceleration, and the increase of hydration products effectively increased the plastic viscosity.
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Woesz, Alexander, James C. Weaver, Murat Kazanci, Yannicke Dauphin, Joanna Aizenberg, Daniel E. Morse, and Peter Fratzl. "Micromechanical properties of biological silica in skeletons of deep-sea sponges." Journal of Materials Research 21, no. 8 (August 1, 2006): 2068–78. http://dx.doi.org/10.1557/jmr.2006.0251.
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The silica skeleton of the deep-sea sponge Euplectella aspergillum was recently shown to be structured over at least six levels of hierarchy with a clear mechanical functionality. In particular, the skeleton is built of laminated spicules that consist of alternating layers of silica and organic material. In the present work, we investigated the micromechanical properties of the composite material in spicules of Euplectella aspergillum and the giant anchor spicule of Monorhaphis chuni. Organic layers were visualized by backscattered electron imaging in the environmental scanning electron microscope. Raman spectroscopic imaging showed that the organic layers are protein-rich and that there is an OH-enrichment in silica near the central organic filament of the spicule. Small-angle x-ray scattering revealed the presence of nanospheres with a diameter of only 2.8 nm as the basic units of silica. Nanoindentation showed a considerably reduced stiffness of the spicule silica compared to technical quartz glass with different degrees of hydration. Moreover, stiffness and hardness were shown to oscillate as a result of the laminate structure of the spicules. In summary, biogenic silica from deep-sea sponges has reduced stiffness but an architecture providing substantial toughening over that of technical glass, both by structuring at the nanometer and at the micrometer level.
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Liu, Yang, Lou Chen, Keren Zheng, and Qiang Yuan. "Improving Environmental Efficiency of Reverse Filling Cementitious Materials through Packing Optimization and Fiber Incorporation." Molecules 26, no. 3 (January 27, 2021): 647. http://dx.doi.org/10.3390/molecules26030647.
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To improve the environmental efficiency of the reverse filling system, three strategies aim to optimize the packing density, and the mechanical property were adopted in this study. Based on the compressive packing model (CPM), the relationship between the D50 ratio and maximum theoretical packing density for a reverse filling system with 25% and 30% superfine Portland cement was established. For comparison, silica fume and steel fiber were also added to the reverse filling system, respectively. The improvement of packing density by adjusting the D50 ratio was verified through the minimum water demand method, CPM, and modified Andreasen and Andersen (MAA) model. Compared to the reverse filling system added with 3 wt % silica fume, which possesses a comparable mechanical property with the optimized group (adjusted D50 ratio), the incorporation of steel fiber shows a more significant increase. The environmental efficiency of all the samples was quantified into five aspects through the calculation based on the mix proportion, compressive strength, and hydration degree. The comprehensive evaluation demonstrated that the optimized reverse filling system exerts a lower environmental impact and possesses a much higher cement use efficiency compared to the majority of ultra-high performance concrete (UHPC)/ ultra-high performance fiber-reinforced concrete (UHPFRC) reported in published papers.
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Dvorkin, Leonid, Nataliya Lushnikova, Oleksandr Bezusyak, Mohammed Sonebi, and Jamal Khatib. "Hydration characteristics and structure formation of cement pastes containing metakaolin." MATEC Web of Conferences 149 (2018): 01013. http://dx.doi.org/10.1051/matecconf/201814901013.
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Metakaolin (MK) is one of the most effective mineral admixtures for cement-based composites. The deposits of kaolin clays are wide-spread in the world. Metakaolin is comparable to silica fume as an active mineral admixture for cement-based composites. In this paper, the rheological and mechanical properties of cement paste containing metakaolin are investigated. The effect of MK is more evident at “tight” hydration conditions within mixtures with low water-cement ratio, provided by application of superplasticizers. The cement is replaced with 0 to 15% metakaolin, and superplasticizer content ranged from 0 to 1.5% by weight of cementitious materials (i.e. cement and metakaolin). An equation is derived to describe the relationship between the metakaolin and superplasticizer content and consistency of pastes. There is a linear dependence between metakalolin content and water demand. Second-degree polynomial describe the influence of superplasticizer content. The application of SP and MK may produce cement-water suspensions with water-retaining capacity at 50-70% higher than control suspensions. The investigation of initial structure forming of cement pastes with SP-MK composite admixture indicates the extension of coagulation structure forming phase comparing to the pastes without additives. Crystallization stage was characterized by more intensive strengthening of the paste with SP-MK admixture comparing to the paste without admixtures and paste with SP. Results on the porosity parameters for hardened cement paste indicate a decrease in the average diameter of pores and refinement of pore structure in the presence of metakaolin. A finer pore structure associated with an increase in strength. X-ray analysis data reveal a growing number of small-crystalline low-alkaline calcium hydrosilicates and reducing portlandite content, when MK dosage increases. Scanning electron microscopy (SEM) data confirm, that hardened cement paste containing MK has crystalline structure with dominance of partially crystalized hydrosilicates and gel-like formations.
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Park, Solmoi, Jun Kil Park, Namkon Lee, and Min Ook Kim. "Exploring Structural Evolution of Portland Cement Blended with Supplementary Cementitious Materials in Seawater." Materials 14, no. 5 (March 4, 2021): 1210. http://dx.doi.org/10.3390/ma14051210.
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The present study investigated the structural evolution of Portland cement (PC) incorporating supplementary cementitious materials (SCMs) exposed to seawater. The samples were made with replacing Portland cement with 10 mass-% silica fume, metakaolin or glass powder. The reaction degree of SCMs estimated by the portlandite consumption shows that metakaolin has the highest reaction degree, thus metakaolin-blended PC exhibits the highest strength. The control exposed to seawater exhibited 14.82% and 12.14% higher compressive strengths compared to those cured in tap water at 7 and 28 days. The samples incorporating metakaolin showed the highest compressive strength of 76.60 MPa at 90 days tap water curing and this was 17% higher than that of the control. Exposure to seawater is found to retard the rate of hydration in all SCM-incorporating systems, while the strength development of the neat PC system is enhanced. The main reaction product that forms during exposure to seawater is Cl-AFm and brucite, while it is predicted by the thermodynamic modelling that a significant amount of M-S-H, calcite and hydrotalcite is to form at an extended period of exposure time.
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Peng, Yan Zhou, Wen Yang, and Qiao Sheng Zhu. "Effect of Heat-Curing Procedure on Strength and Microstructure of Reactive Powder Concrete Having High Volume of Mineral Admixtures." Applied Mechanics and Materials 204-208 (October 2012): 3989–93. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.3989.
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The effect of heat-curing procedure on strength of reactive powder concrete (RPC) having high volume of mineral admixtures, such as ultra-fine fly ash (UFFA), steel slag powder (SS) and silica fume (SF) was studied in this paper. Moreover, the effect of the cuing temperature (20°C, 60°C and 90°C) and the duration (1 day and 3 days) of heat-curing both on microstructure of RPCs’ samples were investigated by SEM-EDXA. The results indicate that the heat-curing procedure has a great influence on strength of this RPC; the compressive strength of specimens cured in a appropriate condition could achieve more than 190 MPa. Moreover, a high curing temperature or a long duration of heat-curing will cause not only a high degree of pozzolanic reaction but also a low n(Ca)/n(Si) ratio of hydration product. Thus, the microstructure of the paste becomes more compact, which would definitely improve the mechanic properties of the hardened paste.
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Song, Keum-Il, Jin-Kyu Song, Bang Yeon Lee, and Keun-Hyeok Yang. "Carbonation Characteristics of Alkali-Activated Blast-Furnace Slag Mortar." Advances in Materials Science and Engineering 2014 (2014): 1–11. http://dx.doi.org/10.1155/2014/326458.
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Alkali-activated ground granulated blast-slag (AAS) is the most obvious alternative material for ordinary Portland cement (OPC). However, to use it as a structural material requires the assessment and verification of its durability. The most important factor for a durability evaluation is the degree of carbonation resistance, and AAS is known to show lower performance than OPC. A series of experiments was conducted with a view to investigate the carbonation characteristics of AAS binder. As a consequence, it was found that the major hydration product of AAS was calcium silicate hydrate (CSH), with almost no portlandite, unlike the products of OPC. After carbonation, the CSH of AAS turned into amorphous silica gel which was most likely why the compressive strength of AAS became weaker after carbonation. An increase of the activator dosage leads AAS to react more quickly and produce more CSH, increasing the compaction, compressive strength, and carbonation resistance of the microstructure.
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Sánchez, Pedro A., Martin Vögele, Jens Smiatek, Baofu Qiao, Marcello Sega, and Christian Holm. "PDADMAC/PSS Oligoelectrolyte Multilayers: Internal Structure and Hydration Properties at Early Growth Stages from Atomistic Simulations." Molecules 25, no. 8 (April 17, 2020): 1848. http://dx.doi.org/10.3390/molecules25081848.
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We analyze the internal structure and hydration properties of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) oligoelectrolyte multilayers at early stages of their layer-by-layer growth process. Our study is based on large-scale molecular dynamics simulations with atomistic resolution that we presented recently [Sánchez et al., Soft Matter 2019, 15, 9437], in which we produced the first four deposition cycles of a multilayer obtained by alternate exposure of a flat silica substrate to aqueous electrolyte solutions of such polymers at 0.1M of NaCl. In contrast to any previous work, here we perform a local structural analysis that allows us to determine the dependence of the multilayer properties on the distance to the substrate. We prove that the large accumulation of water and ions next to the substrate observed in previous overall measurements actually decreases the degree of intrinsic charge compensation, but this remains as the main mechanism within the interface region. We show that the range of influence of the substrate reaches approximately 3 nm, whereas the structure of the outer region is rather independent from the position. This detailed characterization is essential for the development of accurate mesoscale models able to reach length and time scales of technological interest.
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Gun’ko, V. M. "Morphologic and textural effects of gelation and mechanochemical activation on dry or wetted simple and complex nanooxides." Himia, Fizika ta Tehnologia Poverhni 13, no. 4 (December 30, 2022): 361–82. http://dx.doi.org/10.15407/hftp13.04.361.
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The characteristics and properties of fumed oxides depend strongly on various external actions that is of importance from a practical point of view. Therefore, gelation or high-pressure cryogelation (HPC) of aqueous media pure or with 0.1 M NaCl, and mechanochemical activation (MCA) of dry or wetted powders of individual (silica, alumina, their mechanical blends) and complex (silica/titania, alumina/silica/titania, AST1, AST1/A–300) nanooxides were studied to analyze the influence of the nanooxide composition, particulate morphology, and preparation conditions on changes in the morphological and textural characteristics of treated samples. The temperature-pressure behavior of different phases (silica, alumina, and titania) under HPC can result in destroy of complex core-shell nanoparticles (100–200 nm in size) in contrast to small nonporous nanoparticles, NPNP (5–20 nm). The textural characteristics of nanooxides are sensitive to any external actions due to compaction of such supra-NPNP structures as aggregates of nanoparticles, agglomerates of aggregates, and visible structures in powders. The compaction of supra-NPNP enhances the pore volume but much weakly affects the specific surface area (with one exception of AST1) because small NPNP are relatively stable during any external actions (HPC, MCA). The compacted materials are characterized by enhanced mesoporosity shifted to macroporosity with decreasing specific surface area and increasing sizes of nanoparticles or to mesopores with increasing MCA time or amounts of water in wetted powders. At low hydration of the A–300 powder (h = 0.5 g/g), the value of SBET slightly increases if MCA is provided by stirring or ball-milling. Diminution of the freezing temperature from 208 to 77.4 K during HPC results in enhanced compaction of aggregates and agglomerates but this does not practically affect the primary nanoparticles. The degree of decomposition of core-shell nanoparticles of AST1 does not practically increase with decreasing freezing temperature from 208 to 77.4 K. Decomposition of core-shell AST1 particles is inhibited under HPC by added A–300 (1 : 1) working as a damper.
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Ning, Feng Wei, Yue Bo Cai, Yin Bai, Bo Chen, and Feng Zhang. "Effect of expansive agent and internal curing agent on crack resistance of C50 silica fume wet-mix shotcrete." Advances in Mechanical Engineering 11, no. 1 (January 2019): 168781401881916. http://dx.doi.org/10.1177/1687814018819167.
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High-strength shotcrete is always needed to strengthen rock support. However, it will reversely increase the crack risk. Crack normally goes against the durability and shortens the service life of shotcrete. The objective of this article was to improve the crack resistance of shotcrete with expansive agent and internal curing agent. C50 shotcrete with 10% of silica fume was taken as reference mix composition. Ring test and thermal stress test simulating actual temperature, relative humidity, and constraint were carried out to directly assess crack resistance. Restrained deformation, autogenous volume deformation, and pore structure were measured to study how expansive agent and internal curing agent resisted crack. The results indicated that 4% of expansive agent was enough to improve crack resistance of C50 shotcrete. It could fill internal pores and produce compressive pre-stress at earlier age which could be used to compensate shrinkage at later age. Furthermore, the crack resistance of C50 shotcrete could be further promoted when internal curing agent was employed together with expansive agent. The internal curing agent was able to reduce auto-shrinkage by decreasing the loss of internal relative humidity. In addition, it could also enhance the hydration degree of expansive agent, which would strengthen the role of expansive agent on resisting crack.
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Nalaskowski, Jakub, Jarosław Drelich, Jan Hupka, and Jan D. Miller. "Adhesion between Hydrocarbon Particles and Silica Surfaces with Different Degrees of Hydration As Determined by the AFM Colloidal Probe Technique." Langmuir 19, no. 13 (June 2003): 5311–17. http://dx.doi.org/10.1021/la026911z.
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Gołek, Łukasz, Wojciech Szudek, Monika Błądek, and Monika Cięciwa. "The influence of ground waste glass cullet addition on the compressive strength and microstructure of Portland cement pastes and mortars." Cement Wapno Beton 25, no. 6 (2020): 480–94. http://dx.doi.org/10.32047/cwb.2020.25.6.5.
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The paper presents a study on the infl uence of ground waste glass cullet, introduced as a component of Portland cements in the amounts of 5% and 35% by mass, on the properties of pastes and mortars. The pozzolanic nature of the additive was confirmed – the long-term compressive strength of cement composites has incre-ased, compared to the reference sample. However, a decrease in the early compressive strength was observed. Replacing part of the Portland clinker with ground waste glass cullet resulted in the reduction of the heat of hydration. It was determined that the degree of grinding has a signifi cant impact on the activity of waste glass cullet – in the case of the cullet ground to 5000 cm2/g, the beginning of the pozzolanic reaction was observed after 7 days, whereas for the cullet ground to 3000 cm2/g, the reaction was severely delayed. In the course of one year, no negative impact of the alkali-silica reaction on the strength and microstructure of mortars and pastes was observed, however, a longer study needs to be conducted to verify the results. The research proves that waste glass cullet can be potentially used as a main component of Portland cements, with no adverse effects on the properties of the composites.
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Wendner, Roman, Kresimir Nincevic, Ioannis Boumakis, and Lin Wan. "Age-Dependent Lattice Discrete Particle Model for Quasi-Static Simulations." Key Engineering Materials 711 (September 2016): 1090–97. http://dx.doi.org/10.4028/www.scientific.net/kem.711.1090.
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For decades, concrete plays an important role worldwide as a structural material. Construction planning and reliability assessment require a thorough insight of the effects that determine concrete lifetime evolution. This study shows the experimental characterization as well as the results of subsequent aging simulations utilizing and coupling a Hygro-thermo-chemical (HTC) model and the Lattice Discrete Particle Model (LDPM) with aging effects for concretes at various early ages. The HTC component of the computational framework allows taking into account any form of environmental curing conditions as well as known material constituents and predicts the level of concrete maturity. Mechanical response and damage are captured by the well-established LDPM, which is formulated in the framework of discrete meso-scale constitutive models. The chemo-mechanical coupling is accomplished by a set of aging functions that link the meso-scale material properties to an effective aging degree, accounting for cement hydration, silica fume reaction, polymerization, and temperature effects. After introducing the formulations the framework is applied to experimental data of 3 standard low and higher strength concretes. Investigated tests include two types of unconfined compression, Brazilian splitting, three-point-bending, and wedge splitting. Following the model calibration the framework is validated by purely predictive simulations of structural level experimental data obtained at different ages for the same concretes.
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Cunha, A. L. C., J. P. Gonçalves, and J. Dweck. "Evaluating the Pozzolanic Activity of Spent Catalyst Partially Substituting Type II Portland Cement." Key Engineering Materials 634 (December 2014): 131–38. http://dx.doi.org/10.4028/www.scientific.net/kem.634.131.
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The catalyst discarded from fluidized catalytic cracking (FCC) units of heavy oil fractions presents in its composition typically high concentrations of silica and alumina, which give to it the possibility to be used as a pozzolanic material. The pozzolanic activity of a spent FCC catalyst from a Brazilian refinery oil was evaluated by studying the influence of the substitution in different degrees of a type II cement, by this catalytic residue on the hydration process and on the compressive strength of the formed materials. The influence of different particle size fractions of the residue and of its milling process was studied as well. The pozzolanic activity was evaluated by thermogravimetry (TG), derivative thermogravimetry (DTG) and non-conventional differential-thermal analysis (NCDTA). The results show that the chemical pozzolanic activity is enhanced when the sample presents a higher specific surface, as well as, the milling of the residue it is fundamental in order to be accepted and used as a pozzolanic material on partial substitution to cement.
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Lesovik, Valery S., N. V. Chernysheva, and M. Yu Drebezgova. "Properties of Composite Gypsum Binders Depending on Multicomponent Mineral Additives." Materials Science Forum 945 (February 2019): 238–43. http://dx.doi.org/10.4028/www.scientific.net/msf.945.238.
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This article considers the possibility of increasing the effectiveness of composite gypsum binders (CGB) by controlling the processes of structure formation as a result of using new types of multicomponent mineral additives that are significantly different from the traditionally used quartz raw materials:- waste of wet magnetic separation of ferrous quartzites (WMS waste,) of polymineral composition with quartzy of varying degrees of crystallinity, nanodispersed silica and chalk powder. We have studied the cause-effect relationship between the change in the ratio of binding and mineral additives of various compositions, which determines the conditions for the formation of technological and strength characteristics of the projected composite materials with specified performance properties. We have established the presence of regularities in the changes in the properties of CGB, the composition of the hardening products and the microstructure depending on the type and content of gypsum binders of β-and α-modifications, portland cement, multicomponent finely-dispersed mineral additives, the regularity consists in the binding of portlandite, which is released upon portland cement hydration, by the amorphous phase of earth siliconas a part ofnanodispersed powder and chalcedony variety of quartz waste of wet magnetic separation of ferruginous quartzites. This provides a reduction in the basicity of the solidifying system, the intensification of crystal formation, and the formation of newgrowths with a high content of tobormorite-low-basic calcium hydrosilicates that compact the microstructure of the hardening matrix and, as a result, increase the water resistance and stability. It is noted that this mechanism of hydration of CGB minimizes inner stresses and volume deformations, therefore the number of microcracks decreases, which leads to an increase in its efficiency in comparison with the traditionally used gypsum binder and that differs from the traditional portland cement by a fast strength generation.
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Nicolai, Eleonora, Velia Minicozzi, Luisa Di Paola, Rosaria Medda, Francesca Pintus, Giampiero Mei, and Almerinda Di Venere. "Symmetric versus Asymmetric Features of Homologous Homodimeric Amine Oxidases: When Water and Cavities Make the Difference." Symmetry 14, no. 3 (March 3, 2022): 522. http://dx.doi.org/10.3390/sym14030522.
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Symmetry is an intrinsic property of homo-oligomers. Amine oxidases are multidomain homodimeric enzymes that contain one catalytic site per subunit, and that share a high homology degree. In this paper, we investigated, by fluorescence spectroscopy measurements, the conformational dynamics and resiliency in solutions of two amine oxidases, one from lentil seedlings, and one from Euphorbia characias latex, of which the crystallographic structure is still unknown. The data demonstrate that slight but significant differences exist at the level of the local tridimensional structure, which arise from the presence of large internal cavities, which are characterized by different hydration extents. Molecular dynamics and a contact network methodology were also used to further explore, in silico, the structural features of the two proteins. The analysis demonstrates that the two proteins show similar long-range symmetrical connectivities, but that they differ in their local (intra-subunit) contact networks, which appear mostly asymmetric. These features have been interpreted to suggest a new rationale for the functioning of amino oxidases as obligate homodimers.
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Kharchenko, Aleksey I., Vyacheslav A. Alekseev, Igor’ Ya Kharchenko, and Dmitriy A. Bazhenov. "Structure and properties of fine concretes based on composite binders." Vestnik MGSU, no. 3 (March 2019): 322–31. http://dx.doi.org/10.22227/1997-0935.2019.3.322-331.
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Introduction. Wide introduction of fine concretes in the practice of monolithic building construction is limited by their low crack resistance due to considerable shrinkage. To reduce the shrinkage adverse effect on structure and properties of the fine concretes, it is suggested to use for their preparation composite binders, including expanding sulphoaluminate-based cements. Using the fine concrete with enhanced physical and technical properties improves produceability of construction, reduces labor input of concrete casting and allows building installations of complicated architectural forms. Material and methods. To study processes of fine concrete structure formation and properties, concrete mixes were prepared on the base of medium silica sand, dispersed ash entrainment and expanding additive. Activity of the ash entrainment increased at the expense of mechanical and chemical activation. Dispersity of the particles was monitored by means of laser granulometry. The composite binder was prepared by means of thorough homogenization of the basic CEM 42.5 Portland cement and different sorts of mineral aggregates, including an expanding additive based on calcium sulphoaluminate. Maturing conditions at a certain moisture content were simulated for every composition with subsequent evaluation of concrete performance. Results. Results of the study include effect of different mineral additives distinguishing in mineral composition, dispersivity and degree of hydraulic activity on shrinkage amount and kinetics, fine concrete porous structure parameters and strength. It is understood that amount of expansion has an effect on porous structure characteristics of the fine concrete and its strength performance. The study assessed an influence of maturing conditions on the various-composition fine concrete. A considerable influence of maintaining optimal moisture content during hydration on fine concrete technical properties is committed. Conclusions. It is understood that introduction of up to 10 % of expanding sulphoaluminate-based component in basic Portland cement allows to obtain fine concrete with enhanced crack resistance, impenetrability and longevity.
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Tosca, N. J., and A. L. Masterson. "Chemical controls on incipient Mg-silicate crystallization at 25°C: Implications for early and late diagenesis." Clay Minerals 49, no. 2 (April 2014): 165–94. http://dx.doi.org/10.1180/claymin.2014.049.2.03.
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AbstractMg-silicate minerals (e.g., stevensite, kerolite, talc, sepiolite) play an important role in the construction of facies models in lacustrine and peri-marine environments because they are sensitive to changes in solution chemistry. However, the response of Mg-silicate mineralogy to changing aqueous chemistry is only broadly understood because the mechanisms underpinning the coprecipitation of Mg2+and SiO2(aq) from surface water, and subsequent Mg-silicate crystallization, are unclear. Here we describe the results of experiments designed to systematically examine the effects of pH, Mg/Si and salinity of the parent solution on the nature of initially precipitated products. Structural interrogation of the products with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA) allow comparison of synthetic products with naturally occurring crystalline counterparts. In general, Mg2+and SiO2(aq) co-precipitation and nucleation of Mg-silicate layer structures first involves the rapid formation of 2:1 layers with trioctahedral occupancy and a mean coherent X-ray scattering domain between 1–2 unit cells with respect to thecaxis. Well defined but diffusehkreflections indicate two-dimensional growth, turbostratic stacking and highly variable interlayer hydration. Diffuse reflectance FTIR shows numerous structural similarities with stevensite, kerolite and sepiolite. However, TGA/DTA analysis indicates the presence of variable kerolite/stevensite interstratification not readily detectable through XRD analyses, as well as a significant degree of surface and interlayer hydration (e.g. 15–20 wt.%).We observe a number of clear trends in the products with respect to solution chemistry. For example, at low salinity, kerolite-like products dominate at high Mg/Si and high pH, whereas sepiolite-like products are formed at lower pH and lower Mg/Si. At high salinity and high Mg/Si, stevensite-like products are favoured at high pH and kerolite-like products dominate at lower pH, whereas a decrease in Mg/Si of the solution leads to sepiolite-like products at low pH and only stevensite-like products at high pH. Higher pH leads to an increase in octahedral vacancies which favour stevensite-like products; this may result from a higher rate of two-dimensional tetrahedral sheet expansion relative to the octahedral sheet, as inferred from studies of silica oligomerization and brucite growth kinetics.Together, our results indicate that the neoformation of Mg-rich silicates from solution may often begin with the rapid nucleation of hydrated 2:1 layers. Subsequent dehydration leads to progressive layer stacking order and could occur in response to wetting/drying cycles, prolonged exposure to high salinity solutions, or burial and heating. The surface and interlayer water associated with these products is undoubtedly an important source of diagenetic water in Mg-silicate-bearing successions, and the chemistry of this water upon later diagenesis should be a focus of future investigation.
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Pietruś, Wojciech, Rafał Kurczab, and Dariusz Latowski. "The influence of dihydroxyacetone (DHA) contained in the self-tanning lotions with human skin – spectroscopic and theoretical studies." Science, Technology and Innovation 4, no. 3 (October 11, 2017): 79–90. http://dx.doi.org/10.5604/01.3001.0010.8019.
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The purpose of this study was to investigate selected properties of eight bronzers differing in consistency and dihydroxyacetone (DHA) content. The investigated bronzers were divided into three groups including: liquid sunless tanning products containing DHA level of about 15%, half-liquid self-tanners (spray or foam), and bronzers in the form of a cream. The products from the two latter groups contained about 5% DHA. This study inspected if self-tanners have the ability to absorb UV radiation. The aim of using infrared spectroscopy was to investigate the influence of self-tanners on skin moisture level. During the study, quantum-mechanical calculations were done. The calculations were related to computer-based modeling of DHA permeability through the beta-keratin layer of the skin. The calculations were also done to estimate hydrogen bond energy between chains of the beta-keratin as well as the surface of the crystallized beta-keratin surface. The results indicated that DHA absorbed UV-C radiation very strong, whereas UV-B radiation was absorbed to a lower degree. The least absorbancy was discovered in the UV-A range. Liquid and, partly, half-liquid self-tanners reduced skin moisture; however, products in the form of cream contained moisturizing substances that neutralize the negative effect of DHA on skin hydration. In silico studies indicated that DHA does not permeate through the beta-keratin layer of the skin. Potential reasons for this may be the large energy of hydrogen bonds and charged beta-keratin surface.
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Wang, Xiao Jun, Xiao Yao Wang, Hong Fei Zhu, and Xiao Ye Cong. "The Change of Silica Tetrahedron in Cement-Silica Fume Blends Hydration." Materials Science Forum 743-744 (January 2013): 280–84. http://dx.doi.org/10.4028/www.scientific.net/msf.743-744.280.
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The change of silica tetrahedron in cement-silica fume blends hydration is critical for blended cement application. 29Si solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) investigations on the change of silica tetrahedron, which were Portland cement hydration, silica fume in simulated hydration and cement-silica fume blends hydration, were characterized and compared in this paper. The experimental results revealed that the amorphous silica tetrahedron structure in silica fume changed into Q1 and Q2 silica tetrahedrons, the same as silica-oxide structure of cohesive gel in the hydration of Portland cement. The coexistence of Q1 and Q2 silica tetrahedron in hydration product was beneficial to the strength increase of blend paste with silica fume. The amount of Q2 silica tetrahedron in cement-silica fume blends was higher than that in Portland cement. The pozzolanic reaction of silica fume accelerated the course of the silica tetrahedron in blended paste turning into the stable state of Q2 silica tetrahedron and existing principally in blended paste. That is reason that the physical properties of cement-silica fume blends are better than those of Portland cement.
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Rai, Sarita, and Shivani Tiwari. "Nano Silica in Cement Hydration." Materials Today: Proceedings 5, no. 3 (2018): 9196–202. http://dx.doi.org/10.1016/j.matpr.2017.10.044.
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Kim, Byung-Jun, Geon-Wook Lee, and Young-Cheol Choi. "Hydration and Mechanical Properties of High-Volume Fly Ash Concrete with Nano-Silica and Silica Fume." Materials 15, no. 19 (September 23, 2022): 6599. http://dx.doi.org/10.3390/ma15196599.
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This study investigated the effects of nano-silica (NS) and silica fume (SF) on the hydration reaction of high-volume fly ash cement (HVFC) composites. In order to solve the dispersibility problem caused by the agglomeration of NS powder, NS and NSF solutions were prepared. NS content and SF content were used as main variables, and an HVFC paste was prepared in which 50% of the cement volume was replaced by fly ash (FA). The initial heat of hydration was measured using isothermal calorimetry to analyze the effects of NS and SF on the initial hydration properties of the HVFC. In addition, the compressive strength was analyzed by age. The refinement of the pore structure by the nanomaterial was analyzed using mercury intrusion porosimetry (MIP). The results show that the addition of NS and SF shortened the setting time and induction period by accelerating the initial hydration reaction of HVFC composites and improved the compressive strength during the initial stage of hydration. In addition, the micropore structure was improved by the pozzolanic reaction of NS and SF, thereby increasing the compressive strength during the middle stage of hydration.
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Argyris, Dimitrios, David R. Cole, and Alberto Striolo. "Hydration Structure on Crystalline Silica Substrates." Langmuir 25, no. 14 (July 21, 2009): 8025–35. http://dx.doi.org/10.1021/la9005136.
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Ding, Qing Jun, Yu Wang, and Xiu Lin Huang. "Hydration Characteristics and Hydration Products of Tricalcium Silicate Doped with Superplasticizer and Silica Fume." Advanced Materials Research 233-235 (May 2011): 2589–94. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2589.
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By using XRD, isothermal microcalorimetry, ESEM, EDS, NMR, the effects silica fume and polycarboxylate superplasticizer (PC) on the hydration behavior of tricalcium silicate (C3S) paste were researched. The results show that: PC suppresses the hydration of C3S while silica fume promotes the hydration of C3S by consumption of generated Ca(OH)2. Both PC and silica fume change the morphology of hydration products C-S-H gel from needle-bar-like to reunion-like, along with the polymerization state of silicon-oxygen tetrahedron varied greatly. Especially silica fume significantly affects Q1, Q2 percentage of silicon-oxygen tetrahedron.
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Ma, Li Guo, and Yun Sheng Zhang. "Study on the Effect of Fly Ash or Silica Fume to Hydration Heat of Cement." Advanced Materials Research 250-253 (May 2011): 4001–4. http://dx.doi.org/10.4028/www.scientific.net/amr.250-253.4001.
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The hydration heat evolution process is studied on the pure cement paste, the cement- fly ash binary system and the cement- silica fume binary system with water binder ratio(w/b) of 0.53, 0.35 and 0.23 by using isothermal calorimeter(TAM Air). The fly ash replacement in the cement-fly ash binary system is 10%, 30% and 50% respectively. The silica fume replacement in cement-silica fume binary system is 4%, 8% and 12% respectively. The experiments results indicate that w/b had great impact on the hydration heat evolution and the hydration heat decrease with the decrease in w/b. The addition of fly ash greatly decrease the exothermic rate and total hydration heat. The addition of silica fume shortens dormant period and increases the peak exothermic rate, but reduces the total hydration heat.
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Schrader, Alex M., Jacob I. Monroe, Ryan Sheil, Howard A. Dobbs, Timothy J. Keller, Yuanxin Li, Sheetal Jain, M. Scott Shell, Jacob N. Israelachvili, and Songi Han. "Surface chemical heterogeneity modulates silica surface hydration." Proceedings of the National Academy of Sciences 115, no. 12 (March 5, 2018): 2890–95. http://dx.doi.org/10.1073/pnas.1722263115.
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An in-depth knowledge of the interaction of water with amorphous silica is critical to fundamental studies of interfacial hydration water, as well as to industrial processes such as catalysis, nanofabrication, and chromatography. Silica has a tunable surface comprising hydrophilic silanol groups and moderately hydrophobic siloxane groups that can be interchanged through thermal and chemical treatments. Despite extensive studies of silica surfaces, the influence of surface hydrophilicity and chemical topology on the molecular properties of interfacial water is not well understood. In this work, we controllably altered the surface silanol density, and measured surface water diffusivity using Overhauser dynamic nuclear polarization (ODNP) and complementary silica–silica interaction forces across water using a surface forces apparatus (SFA). The results show that increased silanol density generally leads to slower water diffusivity and stronger silica–silica repulsion at short aqueous separations (less than ∼4 nm). Both techniques show sharp changes in hydration properties at intermediate silanol densities (2.0–2.9 nm−2). Molecular dynamics simulations of model silica–water interfaces corroborate the increase in water diffusivity with silanol density, and furthermore show that even on a smooth and crystalline surface at a fixed silanol density, adjusting the spatial distribution of silanols results in a range of surface water diffusivities spanning ∼10%. We speculate that a critical silanol cluster size or connectivity parameter could explain the sharp transition in our results, and can modulate wettability, colloidal interactions, and surface reactions, and thus is a phenomenon worth further investigation on silica and chemically heterogeneous surfaces.
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Yajun, J. "Simulation of silica fume blended cement hydration." Materials and Structures 37, no. 270 (May 27, 2004): 397–404. http://dx.doi.org/10.1617/12684.
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Georgescu, Maria, and Alina Badanoiu. "Hydration process in 3CaO.SiO2-silica fume mixtures." Cement and Concrete Composites 19, no. 4 (January 1997): 295–300. http://dx.doi.org/10.1016/s0958-9465(97)00021-8.
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Yogendran, V., B. W. Langan, and M. A. Ward. "Hydration of cement and silica fume paste." Cement and Concrete Research 21, no. 5 (September 1991): 691–708. http://dx.doi.org/10.1016/0008-8846(91)90164-d.
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Guindy, Nabila M., S. A. Abou El Enien, F. I. El Hosiny, and S. M. A. El Gamal. "Hydration characteristic on lime-silica fume pastes." Journal of Thermal Analysis 40, no. 1 (July 1993): 151–57. http://dx.doi.org/10.1007/bf02546565.
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He, Zhen, Huamei Yang, Shuguang Hu, and Meiyan Liu. "Hydration mechanism of silica fume-sulphoaluminate cement." Journal of Wuhan University of Technology-Mater. Sci. Ed. 28, no. 6 (December 2013): 1128–33. http://dx.doi.org/10.1007/s11595-013-0832-0.
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Yajun, J., and J. H. Cahyadi. "Simulation of silica fume blended cement hydration." Materials and Structures 37, no. 6 (July 2004): 397–404. http://dx.doi.org/10.1007/bf02479636.
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